1. Field of the Invention
The present invention relates to an image reading apparatus having a flow-reading mode in which a sheet being conveyed is read.
2. Description of the Related Art
Image reading apparatuses have at least one of: a fixed-reading mode in which a sheet placed on a platen is read; and a flow-reading mode in which a sheet conveyed by an auto document feeder (ADF) is read. Especially in the flow-reading mode, if dust or glue of sticky notes and the like (such dust or glue is hereafter referred to as “foreign material”) adhering to the platen is read, a linear foreign material image appears in the read image. The U.S. Pat. No. 7,058,236 describes an invention of changing the reading position by moving a mirror table when a foreign material adhering to a platen is detected.
According to the invention in U.S. Pat. No. 7,058,236, whether or not a foreign material is present needs to be checked for each of a plurality of reading position candidates, in a state where no sheet is present on the platen. A certain amount of processing time is required to detect whether or not a foreign material is present for all of the plurality of reading position candidates. Image reading apparatuses in recent years have a sleep mode for saving power. In the sleep mode, whether or not a foreign material adheres to the platen is unclear. Therefore, the need for the foreign material detection process is high upon return from the sleep mode. Upon return from the sleep mode, however, the user wants to perform flow-reading. If the foreign material detection process and the reading position change process take a long time, the time to complete flow-reading increases, and the usability decreases. In particular, conventionally flow-reading cannot be started until the detection process is completed for all of the plurality of reading position candidates, unless a reading position candidate in which no foreign material is detected is found. The detection process thus tends to take long.